Problem 82 - University Physics with Modern Physics

Question

In another experiment, a piece of the web is suspended so that it can move freely. When either a positively charged object or a negatively charged object is brought near the web, the thread is observed to move toward the charged object. What is the best interpretation of this observation? The web is (a) a negatively charged conductor; (b) a positively charged conductor; (c) either a positively or negatively charged conductor; (d) an electrically neutral conductor.

Step-by-Step Solution

Answer

(d) an electrically neutral conductor.

Step 1: Identify the Phenomenon

When a charged object, either positive or negative, is brought near the web, the web moves toward the object. This suggests that there is an attraction between the web and the charged object.

Step 2: Analyze the Behavior of Conductors

Conductors allow electric charges to move freely across their surface. If an electrically neutral conductor is brought near any charged object, the conductor will experience attraction due to charge induction, making one side slightly positive and the opposite side slightly negative.

Step 3: Apply Charge Induction Theory

When a charged object is near, the side of the neutral conductor closest to the object gains an opposite charge due to induced charge separation. This results in attraction regardless of whether the charged object is positive or negative.

Step 4: Conclude the Assessment

As the web moves toward either a positively or negatively charged object, it aligns with the behavior of a neutral conductor, where charge induction causes attraction to any charged object.

Key Concepts

Electrically Neutral Conductor

An electrically neutral conductor is a material that, while having no net charge, allows electric charges to move freely across its surface. Despite being neutral overall, the presence of a nearby charged object can influence the distribution of the charges on the conductor.
Key characteristics:

• Neutral conductors have an equal number of positive and negative charges.
• They can respond to external electric fields due to the mobility of their charges.
• The net effect is balance, so any external charge presence can cause only a rearrangement, not an addition or subtraction of charge.

When a charged object is brought close, the neutral conductor does not acquire a net charge. Instead, it rearranges its internal charges in response to the external field. This capability of neutral conductors forms the basis for many phenomena observed in electricity and magnetism.

Conductors and Charge Movement

In conductors, electric charges can move freely, allowing them to respond quickly to external electric fields. This movement is crucial for understanding how conductors interact with charged objects brought near them.
Charge Movement Mechanism: When a charged object approaches, the charges within the conductor redistribute to minimize internal energy. If the object is positively charged, electrons in the conductor will move toward the side closest to the object. Conversely, if the object is negatively charged, electrons will move away from the object.

• This redistribution leads to the creation of induced charges: one side of the conductor becomes oppositely charged relative to the charged object.
• This charge separation is governed by principles of electrostatics, aiming for the lowest energy configuration.

Understanding this dynamic movement of charges helps explain why conductors experience forces and movements when in proximity to charged entities.

Attraction due to Charge Induction

Charge induction is a fascinating process where a conductor becomes polarized due to the influence of a nearby charged object, leading to attraction. This happens even if there is no direct contact between the two objects.
Process of Induction:

• When a charged object approaches, it influences the neutral conductor, causing a separation of charges within the conductor.
• The side of the conductor closest to the charged object gains an opposite charge, resulting in an attractive force.

This induced attraction occurs because oppositely charged regions form on the surface of the conductor closest to the external charge. Therefore, the conductor is pulled toward the charged object, explaining why an electrically neutral conductor is drawn to both positively and negatively charged items. Understanding charge induction is key to grasping how seemingly neutral objects can exhibit attractive behavior when exposed to electric fields. This concept is foundational in the study of electrostatics and is critical for fields such as electrical engineering and physics.